There have been angry scenes at the Waterford Crystal plant in Kilbarry after staff were told the company was shutting down.
A statement from the receiver, David Carson of Deloitte, confirmed that 480 of the 670 employees have been made redundant.
The company said this evening that around 190 staff in the manufacturing section would continue to be employed.
The visitors' centre will close for a temporary period.
At least 100 Waterford Crystal employees are refusing to leave the visitors' gallery at the factory tonight and are staging an unofficial sit-in.
The employees say they will not be leaving until they meet with Mr Carson.
There were some scuffles at one point and a main door to the visitors' centre was damaged.
Mr Carson wrote to staff today and informed them that manufacturing will cease with immediate effect at Kilbarry.
In the statement Mr Carson said: 'The decision to cease manufacturing does not necessarily preclude a resumption of operations in Waterford in the future.
'The receiver is continuing negotiations with interested parties with a view to a sale of the company's assets and those discussions are focused on agreeing the terms upon which a transaction could be completed.'
Production at the factory stopped this afternoon and staff had been told to 'expect bad news'.
Waterford Crystal has been in receivership for the past four weeks.
Local Sinn Féin Councillor Joe Kelly, who is one of those currently occupying the visitors' gallery, said the receiver had told staff he would not close the company while there were interested investors.
'Today he has gone back on his word,' he said.
General Secretary of the Irish Congress of Trade Unions David Begg has warned that the move to close Waterford Crystal today could discourage potential investors from buying the plant.
Mr Begg said the news had come as quite a shock, adding that he had been in touch with Waterford Crytsal union representatives and with senior Government officials to see if they can do anything to stop this.
Former CEO to bid for Waterford Crystal
A new offer to buy Waterford Crystal and keep the plant and visitor centre open will be made by a former chief executive of the company.
John Foley told RTÉ News he has joined a US-based consortium that will make a new bid for the company.
Mr Foley, who stood down as CEO of Waterford Crystal after it went into receivership, said the bid was backed by US investment group Clarion Capital.
He said the group believed it could secure ten-year supply and price agreements for Waterford Crystal products.
Also involved in the consortium is Peter Cameron, who is a former CEO of Waterford Wedgwood.
Mr Foley said it was essential that manufacturing was continued at Waterford and the group planned to make an offer for Waterford Crystal in the short term to the receiver.